You start the game with three submarines. Guide
your submarine with the mouse pointer. Press the mouse button to fire
a torpedo upward toward the surface. Press the keyboard space bar
to fire a torpedo to the right. Since it takes your crew some time
to reload the torpedo tubes, you are allowed a maximum of one torpedo
at a time in each direction.

As the submarine captain, you must destroy
all ten of the merchant ships in the top row before you can move on
to your next mission. Try not to torpedo hospital ships. It's a violation
of international law--and the consequences can be pretty immediate.
Skillful maneuvering will be necessary on advanced missions in order
to survive exploding depth charges, hostile torpedo fire, and magnetic
mines.

Your sub has a limited supply of fuel and torpedoes,
and must be resupplied frequently. A supply sub will pass by occasionally
near the ocean bottom and release a trained dolphin carrying fuel
and torpedoes. By making contact with the dolphin's supply pack, you
can resupply your vessel. Whatever you do, don't torpedo the dolphin!
He has many friends in these waters, and they won't take too kindly
to it.